Pedometers and step detectors based on inertial sensors have found various applications in fitness, health monitoring, positioning systems, and more. Step detection in these applications is typically based on sensors that are constrained to a particular position with respect to a pedestrian (e.g., waist, wrist, shoes, etc.). For mobile phones and other mobile devices, step detection can be more difficult because the mobile device can be carried in any of a variety of locations (e.g., a pedestrian's hand, pocket, purse, etc.) and subject to combined motion. Step detection performed when the mobile device is in the hand of a user's swinging arm can be particularly difficult. As such, step detection in mobile devices performed when such swinging is occurring can be highly inaccurate.